As a matter of fact, mass terror and purges were even more central to the Soviet system of rule than to Nazism, the full extent of whose tyranny did not evolve until several years after Hitler had taken power, and then in the midst of World War II. Soviet mass terror, by contrast, was a feature of the regime right from the beginning. Lenin's core principle of Red Terror was applied in the slaughter of up to half a million class enemies in the very first years of Soviet rule. And that is before we add in the millions of...